Conventional drop-on-demand inkjet printers are commonly categorized based on one of two mechanisms of drop formation within the inkjet printhead. A thermal bubble inkjet printer uses a heating element actuator in an ink-filled chamber to vaporize ink and create a bubble that forces an ink drop out of a nozzle. A piezoelectric inkjet printer uses a piezoelectric material actuator on a wall of an ink-filled chamber to generate a pressure pulse that forces a drop of ink out of the nozzle.
In both cases, after an ink drop is ejected from the ink chamber and out through the nozzle, the chamber is refilled with ink through an ink inlet that provides fluidic communication between the chamber and an ink supply channel. The size of the ink inlet is a result of a compromise between the need to quickly refill the chamber and the need to minimize the back flow of ink into the ink supply channel during the drop ejection or jetting event. A large ink inlet opening provides for a faster refill of the ink chamber, but it also allows a substantial amount of the drop ejection energy generated by the piezo element or thermal resistor element to be lost to the back flow of ink into the ink supply channel. As a result, more ejection energy is required to drive the ink droplets. In addition, a large back flow of ink into the ink supply channel gives rise to pressure oscillations in the supply channel which causes hydraulic cross-talk in adjacent ink chambers.
The sizing of the ink inlet and nozzle relative to one another is generally known as impedance matching. Usually, the size of the ink inlet radius is on the same order of magnitude as the size of the nozzle radius. However, if the size of the inlet radius relative to the size of the nozzle radius is incorrect, there is a poor impedance match which can result in either nozzle starvation (i.e., too little ink ejected through the nozzle) or excessive oscillations in the drop velocity and drop volume, especially as the ejection or jetting frequency is increased.